Surface Relief Formation with Molecular Orientation in Photoreactive Liquid Crystalline Polymer Film

Abstract

Surface relief gratings (SRG) with anisotropic gratings in photo-cross-linkable liquid crystalline (LC) polymethacrylate films comprising 4-(4-methoxycinnamoyloxy)-biphenyl (MCB) side groups were fabricated by irradiating with a linearly polarized ultraviolet (LPUV) light through a grating photomask and subsequent annealing at LC temperature range of the film. A reorientation of the mesogenic groups accompanied the molecular diffusion after the annealing, although the molecular diffusion and the reorientation direction depended on degree of the photoreaction of the mesogenic groups and the polarization (E) of LPUV light. When the degree of the photoreaction was around 7 mol%, molecules moved from illuminated area to non-illuminated area, and the molecular reorientation direction was parallel to the grating line regardless of E of LPUV light. In contrast, the diffusion direction was determined from the non-illuminated area to the illuminated region, and the molecular reorientation direction was always parallel to E of LPUV light when the degree of the photoreaction was around 20 mol%. All the fabricated SRGs showed characteristics of the polarization dependent gratings due to the surface relief formation and the molecular reorientation direction. The diffraction properties of the SRGs were good agreement with theoretical analyses.